Keratoacanthomas are a variant of squamous cell carcinoma which are characterized by rapid progression, a crateriform appearance and sometimes spontaneous resolution. Some dermatologists, such as those I met in France, consider them NOT to be SCCs, but almost without exception here in the U.S. we do consider them to be SCCs. In fact, all of our pathologists report them as "Squamous cell carcinoma, keratoacanthoma type."
Although the splitters among us will describe multiple variants of KAs, they really come in the solitary and the multiple eruptive varieties. We have all seen the patients who get numerous KAs on the legs and arms, and go through periods where they grow lots of them in a short timeframe.
I presented this patient at Grand Rounds at Saint-Louis, and the French trained docs all insisted (after reviewing photomicrographs of the glassy eosinophilic cytoplasm characteristic of KAs) this was a keratoacanthoma, not an SCC and that it should, by nature, involute. Their enthusiasm for this theory waned when I told them the patient died from the tumor via metastases to the brain.
The reason this lesion was so large was that the patient was a member of a religion which proscribed the use of transfusions, and even though the Mohs team assured her she wouldn’t need one, she refused to go under the knife until it was way too late. The only thing she consented to was intralesional bleomycin, which did nothing.
How could you be sure this was not a giant BCC? First, the BCCs are generally glassy or waxy at the edges, or a little translucent if nodular. Second, if they are that large, they are not exophytic but are eroded. Third, the induction of blood vessels would be much more brisk than this KA. Fourth, BCCs don’t have that keratotic core.